The present invention relates generally to the field of manufacture of data storage disks, and in particular, to a method of making multiple optical data storage disk stampers from one master, while maintaining the integrity of data tracks encoded therein.
Optical data storage disks have gained widespread acceptance for the storage, distribution and retrieval of large volumes of information. These disks include audio and video program material, as well as computer programs and data. Formats of optical data disks include audio CD (compact disc), CD-R (CD-recordable), CD-ROM is (CD-read only memory), DVD (digital versatile disk or digital video disk) media, DVD-RAM (random access memory), and various types of rewritable media, such as magneto-optical (MO) disks and phase change optical disks.
In general, optical disks (such as CD-ROMs) are produced by making (e.g., laser recording) a master which has physical features representing the data formed in or on a reference surface therein. The master is used to make a stamper, which, in turn, is used in an injection molding process to make production quantities of replica disks, each containing the data and tracking information which was encoded in the master.
For example, during the injection molding process for CD-ROMs, the stamper data is molded into each disk substrate by the formation of lower reflectance xe2x80x9cpitsxe2x80x9d embossed within a plane of higher reflectance xe2x80x9clandsxe2x80x9d. Typically, the information side of the disk is then coated with a reflectance layer, such as a thin layer of aluminum, and in the case of a CD, followed by a protective layer of lacquer. The data tracks on an optical disk can be arranged in a spiral track originating at the disk center and ending at the disk outer edge, or alternatively, a spiral track originating at the disk outer edge and ending at the disk center. The data can also lie in a series of concentric tracks spaced radially from the disk center.
Several thousand (e.g., 50,000) replica disk substrates may be made using the same stamper. As a result of the pressure and temperature cycling involved in the molding process, stampers become damaged and wear. For most optical data storage disk products, a first generation stamper is made by electroforming or electroplating a recorded master disk. This process is destructive to the recorded master disk, resulting in one stamper per recorded master. Since the cost of making a recorded master disk can be significant, the process yields and lifetime of the stamper account for a significant percentage of the final optical data storage disk cost.
In an attempt to lower manufacturing costs and increase efficiency, processes have been developed to make multiple stampers from one master disk. Conventional processes for making stampers from a master disk include a pyramiding family process. This process involves the making of a xe2x80x9cfatherxe2x80x9d stamper or first generation stamper from the master. The father stamper is used to make a xe2x80x9cmotherxe2x80x9d stamper or second generation stamper. The same process may be repeated using the xe2x80x9cmotherxe2x80x9d stamper to make a xe2x80x9cdaughterxe2x80x9d or third generation stamper.
The process of electroforming multiple generations of stampers has known disadvantages. Conventional processes are destructive to the master disk. At each generation, (father, mother, daughter), a surface treatment is necessary to achieve separation, resulting in a molded replica disk with encoded information having a noise floor increase and a signal quality decrease. Known conventional processes do not work well with optical disks formats where the ratio of pit volume to surface area is small. After completion of the forming process, the encoded data tracks may be damaged when separating the father stamper from a mother stamper (or the mother stamper from a daughter stamper).
In one embodiment, the present invention provides a method of making a stamper for use in a data storage disk molding process. The method includes making a first stamper comprising the steps of providing a stamper body having an information layer thereon, and covering the information layer with a first metal layer. A second stamper is made from the first stamper by covering the first metal layer with a second metal layer to form a stamper assembly. The first metal layer and the second metal layer are bonded together. The first metal layer and the second metal layer are removed from the stamper assembly to form the second stamper. Removal of the first layer and the second layer from the stamper assembly is non-destructive to the information layer.
The first metal layer and the second metal layer are made of the same metal. In one preferred embodiment, the first metal layer and the second metal layer are made of nickel. The step of covering the information layer with the first metal layer includes depositing a relatively thin layer of nickel onto the information layer. The information layer is made of a photopolymer. The step of covering the first metal layer with the second metal layer includes electroplating the second metal layer onto the first metal layer.
In one application, the first stamper is a first generation stamper and the second stamper is a second generation stamper. In another application, the first stamper is a second generation stamper, and the second stamper is a third generation stamper.
In another embodiment, the present invention provides a method which allows the making of multiple optical disk stampers from one recorded master using a second generation process. The method includes providing a recorded master. A first generation stamper is made from the recorded master using a photopolymerization process. A second generation stamper is made from the first generation stamper using an electroplating process, wherein a portion of the first generation stamper becomes part of the second generation stamper.
In a third embodiment, the present invention provides a method which allows the making of multiple optical disk stampers from a recorded master. The method includes recording a master disk. A first generation stamper is made from the master disk using a photopolymerization process. The photopolymerization process includes forming a first stamper body having a photopolymer information layer thereon. The information layer is coated with a first metal layer. A second generation stamper is made from the first generation stamper, including coating the first metal layer with a second metal layer to form a stamper assembly. The first and second metal layers are separated from the stamper assembly to form the second generation stamper, wherein separating the first and second generation stamper from the stamper assembly is non-destructive to the information layer. In one preferred embodiment, the first metal layer and the second metal layer are made of the same metal, and more preferably, the first metal layer and the second metal layer are made of nickel. The step of covering the first metal layer with the second metal layer includes the step of electroplating the second metal layer onto the first metal layer.
The step of recording the master disk may further include providing a glass substrate having a photoresist layer attached to the glass substrate through a bonding layer. An information layer is recorded on the master disk through exposing the photoresist layer to a laser beam, including exposing a portion of the photoresist layer down to the bonding layer to form a master pit.
The step of making a first generation stamper from the master disk may further include sputtering a nickel layer onto an information layer on the master disk. A photopolymer layer is positioned between the nickel layer and the first structural layer using a rolling bead process. The photopolymer layer is cured with an ultra-violet light source. Both the photopolymer and first structural layers are separated from the nickel layer, wherein separation of from the nickel layer is non-destructive to the master disk. A second structural layer is bonded to the first structural layer, and the bonding photopolymer is cured with a UV light source. In one preferred application, the first structural layer is made of polymethylmethacrylate, and the second structural layer is made of glass. A rolling bead process is used to bond the second structural layer to the first structural layer.
In a fourth embodiment, the present invention provides a method of making multiple optical disk stampers from one recorded master using a third generation process. The method includes recording a master disk. A first generation stamper is made from the master disk using an electroplating process. A second generation stamper is made from the first generation stamper using a photopolymerization process. A third generation stamper is made from the second generation stamper using an electroplating process.
The first generation stamper includes an information surface, and making the second generation stamper from the first generation stamper further includes a photopolymer layer between the first generation stamper and a first structural layer using a rolling bead process. The photopolymer layer is cured with an ultra-violet light source. The nickel first generation stamper is separated from the photopolymer layer. A thin nickel coating is put on the information surface. In one application, the first structural layer is made of glass.
The step of making a third generation stamper from the second generation stamper may include coating the photopolymer layer with a first metal layer. The first metal layer is coated with a second metal layer to form a stamper assembly. The first metal layer is separated from the photopolymer layer to form the third generation stamper, wherein separating the first and second metal layers from the stamper assembly is non-destructive to the second generation stamper. In one preferred application, the first metal layer and the second metal layer are formed of the same metal, which is nickel. The step of coveting the first metal layer with the second metal layer includes the step of electroplating the second metal layer onto the first metal layer.